This invention relates to a process for the preparation of 3,5-xylenol from 3,5,5-trimethylcyclohexene-2-one (isophorone).
3,5-xylenol is recognized to be useful as a disinfectant and as a starting material for the preparation of resins, vitamin E, and other compounds, including dyes, agricultural, pharmaceutical and aroma chemicals.
It is known that isophorone can be converted at elevated temperatures to 3,5-xylenol (also known as 3,5-dimethylphenol and as 1,3-dimethyl-5-hydroxybenzene) without the use of a catalyst. However, for good yields of the desired product it is necessary to employ a catalyst, which may be either homogeneous (for example, a halogen or organic halogen compound as described in U.S. Pat. No. 4,086,282) or heterogeneous (for example, certain supported metals or metal compounds as described in U.S. Pat. No. 2,369,197 or Great Britain patent specification Nos. 1,197,803 and 1,451,570).
In principal, a heterogeneous catalyst is typically preferred for the reaction, in order to eliminate problems of catalyst separation from the product 3,5-xylenol. However, use of known heterogeneous catalysts fails to result in the desired selectivities and/or conversions and/or reaction rates. As in all catalytic processes, conversion, selectivity and rate are important from the standpoint of utilization of starting material and catalyst. It is further of particular importance to maximize selectivity and conversion in this process because separation of by-products and isophorone from 3,5-xylenol is difficult. Still further and perhaps most importantly, selectivity is a critical aspect of this conversion because the formation of by-products is accompanied by deactivation of heterogeneous catalysts through buildup of solid carbonaceous deposits, shortening effective catalyst life and dictating frequent regeneration.
Commercially acceptable levels of conversion have been achieved using heterogeneous catalysts comprising cobalt and molybdenum, as are described in the aforementioned Great Britain patent specification No. 1,451,570. However, the selectivity of such catalyst is less than would be desired.
With regard to particular features of the present invention relating to certain rare earth metals as components of catalysts for the conversion of isophorone to 3,5-xylenol, U.S. Pat. No. 2,369,197 makes mention of a cerium containing catalyst, but expresses preference for other metals (i.e., iron, cobalt, and/or chromium). With regard to other features of the invention relating to alkali or alkaline earth metals and to transition metals as catalyst components, U.S. Pat. No. 2,369,197 and Great Britain No. 1,451,570 list certain of such metals, although not in combination with rare earth metals.